每日要点

二维数组

int a[][] = new int[2][3];
二维数组 a 可以看成一个两行三列的数组。

• 例子1:学生的成绩

        int[][] scores = new int[5][3];
        for (int i = 0; i < scores.length; i++) {
            for (int j = 0; j < scores[i].length; j++) {
                scores[i][j] = (int) (Math.random() * 101);
            }
        }

• 例子2:杨辉三角:
  1
  1 1
  1 2 1
  1 3 3 1
  1 4 6 4 1
  1 5 10 10 5 1

         int[][] y = new int[10][];
         for (int i = 0; i < y.length; i++) {
            y[i] = new int[i + 1];
            for (int j = 0; j < y[i].length; j++) {
                if (j == 0 || j == i) {
                    y[i][j] = 1;
                }
                else {
                    y[i][j] = y[i - 1][j] + y[i - 1][j - 1];
                }
                System.out.print(y[i][j] + "\t");
            }
            System.out.println();
        }

面向对象

对象是可以接收消息的实体
特征 :
1.一切都是对象
2.对象都有属性和行为
3.每个对象都是独一无二的
4.对象都属于某个类
类是对象的蓝图和模板
　- 数据抽象 - 属性
　- 构造器 - 创建对象需要使用构造器
　- 行为抽象 - 方法

面向对象编程的第1步 - 定义类

public class Student {
    // 数据抽象 - 属性 - 找名称
    private String name;
    private int age;
    
    // 构造器
    public Student(String n, int a) {
        name = n;
        age = a;
    }
    
    // 行为抽象 - 方法 - 找动词
    public void play(String gameName) {
        System.out.println(name + "正在玩" + gameName + ".");
    }
    
    public void study() {
        System.out.println(name + "正在学习.");
    }
    
    public void watchJapaneseAV() {
        if (age >= 18) {
            System.out.println(name + "正在观看岛国爱情动作片.");
        }
        else {
            System.out.println(name + "只能观看《熊出没》.");
        }
    }
}

**面向对象编程第2步 - 创建对象 **

        // new 构造器();
        Student stu = new Student("王大锤", 15);

面向对象编程第3步 - 给对象发消息

        stu.study();
        stu.play("LOL");
        stu.watchJapaneseAV();
        
        Student stu2 = new Student("张三", 18);
        stu2.study();
        stu2.play("斗地主");
        stu2.watchJapaneseAV();

this 关键字

this 代表这个对象

• 例子:

public class Dog {
    private String nickname;
    private boolean isLarge;
    
    public Dog(String nickname, boolean isLarge) {
        // this 代表这个对象
        this.nickname = nickname;
        this.isLarge = isLarge;
      }

      public void bark() {
        System.out.println(nickname + ": 汪汪汪....");
      }
    
      public void keepTheDoor() {
        if (isLarge) {
            System.out.println(nickname + "正在看门.");
        }
        else {
            System.out.println(nickname + "不能看门.");
        }
      }
   }

主函数:

        Dog dog1 = new Dog("旺财", true);
        dog1.bark();
        dog1.keepTheDoor();
        
        Dog dog2 = new Dog("花花", false);
        dog2.bark();
        dog2.keepTheDoor();

其他内容

写代码的终极原则: 高内聚 低耦合
high cohesion low coupling

1TBS - One True Bracing Style 打{}风格
Allman - FreeBSD

如果定义类时没有写任何一个构造器
那么系统会自动添加一个默认的隐式构造器(平庸构造器)

public Clock() {
    }

写代码低耦合 举例:

System.out.printf("%02d:%02d:%02d\n", hour, minute, second);

这样写代码就跟控制台紧紧耦合在了一起 ,应该这样写:

return String.format("%02d:%02d:%02d", hour, minute, second);

窗口类

JFrame

        // 创建窗口对象
        JFrame f = new JFrame("我的第一个窗口");
        // 通过给窗口对象发消息来设置和显示窗口
        f.setSize(400, 300); // 大小
        f.setLocationRelativeTo(null);  // 窗口摆放
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //关窗口自动关闭程序
        
        Clock clock = new Clock();
        JLabel label = new JLabel(clock.display()); // 创建标签
        label.setHorizontalAlignment(JLabel.CENTER); // 设置水平对齐  - 居中
        Font font = new Font("微软雅黑", Font.BOLD, 36); // 设置字体  
        label.setFont(font); // 将字体添加到标签
        f.add(label); // 将标签添加到窗口
        
        new Timer(1000, new ActionListener() {
            
            @Override
            public void actionPerformed(ActionEvent e) {
                // TODO Auto-generated method stub
                clock.run();
                label.setText(clock.display());
            }
        }).start();
        
        f.setVisible(true); // 显示窗口

昨天作业讲解

• 1.买彩票红色球 1~33　　　　蓝色球 1~16
  01 05 11 17 18 22　　　　 　　05
  08 10 22 23 31 32　　　　　　11
  数字不能重复
  输入 几 随机选出 几组号码

        Scanner input = new Scanner(System.in);
        System.out.print("机选几注: ");
        int n =input.nextInt();
        input.close();
        for (int counter = 1; counter <= n; counter++) {
            int[] redBalls = new int[6];
            for (int i = 0; i < redBalls.length;) {
                // 生成1~33的随机数作为红色球的号码
                int number = (int) (Math.random() * 33 + 1);
                // 检查此号码在之前选中的号码中有没有出现过
                boolean isDuplicated = false;
                for (int j = 0; j < i; j++) {
                    if (redBalls[j] == number) {
                        isDuplicated = true;
                        break;
                    }
                }
                if (!isDuplicated) {
                    redBalls[i] = number;
                    i += 1;
                }
            }
            bubbleSort(redBalls);
            for (int x : redBalls) {
                System.out.printf("%02d ", x);
            }
            int blueBall = (int) (Math.random() * 16 + 1);
            System.out.printf("| %02d\n", blueBall);
        }
    }
    
    public static void bubbleSort(int[] array) {
        // 数组有N个数，需要N-1次循环
        boolean swapped =true;
        for (int i = 1; swapped && i < array.length; i++) {
            swapped = false;
            for (int j = 0;j < array.length - i; j++) {
                if (array[j] > array[j + 1]) {
                    int temp = array[j];
                    array[j] = array[j + 1];
                    array[j + 1] = temp;
                    swapped = true;
                }
            }
        }
    }

例子

• 1.电子钟
  电子钟类:

public class Clock {
    private int hour;
    private int minute;
    private int second;
    
    // 如果定义类时没有写任何一个构造器
    // 那么系统会自动添加一个默认的隐式构造器(平庸构造器)
//  public Clock() {
//  }
    
    public Clock() {
        // 拿系统时间
        // Java 7-
//      Calendar cal = new GregorianCalendar();
//      this.hour = cal.get(Calendar.HOUR_OF_DAY);
//      this.minute = cal.get(Calendar.MINUTE);
//      this.second = cal.get(Calendar.SECOND);
        
        // Java 8+
        LocalDateTime time = LocalDateTime.now();
        this.hour = time.getHour();
        this.minute = time.getMinute();
        this.second = time.getSecond();
    }
    
    public Clock(int hour, int minute, int second) {
        this.hour = hour;
        this.minute = minute;
        this.second = second;
    }
    
    public String display() {
        // 这样写代码就跟控制台紧紧耦合在了一起 
//      System.out.printf("%02d:%02d:%02d\n", hour, minute, second);
        return String.format("%02d:%02d:%02d", hour, minute, second);
    }

    public void run() {
        second += 1;
        if (second == 60) {
            second = 0;
            minute += 1;
            if (minute == 60) {
                minute = 0;
                hour += 1;
                if (hour == 24) {
                    hour = 0;
                }
            }
        }
    }
}

主函数:

        Clock clock = new Clock();
        System.out.println(clock.display());
        while (true) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            clock.run();
            System.out.println(clock.display());
        }

作业

• 1.定义一个类 描述手机 品牌尺寸等 打电话 发短信等
  call send short message install application App
  uninstall / remove update

手机类:

public class MobilePhone {
    private String brand;
    private double size;
    private double price;
    private String phoneModel;
    private String manufacturer;
    private String number;
    
    public MobilePhone(String brand, double size, double price, String phoneModel,
            String manufacturer, String number) {
        this.brand = brand;
        this.size = size;
        this.price = price;
        this.phoneModel = phoneModel;
        this.manufacturer = manufacturer;
        this.number = number;
    }

    public String displayInformation() {
        return String.format("手机信息: \n品牌: " + brand + "\n型号: " + phoneModel
                + "\n制造商: " + manufacturer + "\n尺寸: %.2f寸 \n价格: %.2f元 \n电话号码: "
                + number, size,price);
    }
    
    public String call(String number) {
        return String.format(this.number + " 正在给 " + number + "打电话");
    }
    
    public String sendShortMessage(String number) {
        return String.format(this.number + " 正在给 " + number + "发短信");
    }
    
    public String installAPP(String app) {
        return String.format(this.phoneModel + " 正在安装 " + app);
    }
    
    public String uninstallAPP(String app) {
        return String.format(this.phoneModel + " 正在卸载 " + app);
    }
    
    public String updateAPP(String app) {
        return String.format(this.phoneModel + " 正在更新 " + app);
    }
}

主函数:

        MobilePhone mobilePhone = new MobilePhone("魅族", 5.5, 2000, "魅蓝Note",
                "中国", "18908042994");
        System.out.println(mobilePhone.displayInformation());
        System.out.println(mobilePhone.call("18602132435"));
        System.out.println(mobilePhone.sendShortMessage("18602132435"));
        System.out.println(mobilePhone.installAPP("熊猫TV"));
        System.out.println(mobilePhone.uninstallAPP("UC浏览器"));
        System.out.println(mobilePhone.updateAPP("QQ"));

• 2.写个程序 模拟 奥特曼打小怪兽
  hp mp
  攻击行为
  攻击参数 小怪兽
  奥特曼必杀技
  小怪兽反击
  奥特曼类:

public class Ultraman {
    private String name;
    int hp;
    int mp;
    
    public Ultraman(String name, int hp, int mp) {
        this.name = name;
        this.hp = hp;
        this.mp = mp;
    }

    public void attack(Monster m) {
        m.hp -= 20;
        System.out.println(this.getName() + "普通攻击了" + 
        m.getName());
    }
    
    public void hugeAttack(Monster m) {
        m.hp -= 50;
        System.out.println(this.getName() + "暴击了" + 
                m.getName());
    }
    
    public void magicalAttack(Monster[] mArray) {
        for (Monster m : mArray) {
            m.hp -= 20;
        }
        this.mp -= 100;
        System.out.println(this.getName() + "发动大招攻击了所有小怪兽");
    }
    
    public void status() {
        System.out.printf(this.getName() + " hp:%d mp:%d\n", hp, mp);
    }
    
    public String getName() {
        return this.name;
    }
}

小怪兽类:

public class Monster {
    private String name;
    int hp;
    
    public Monster(String name, int hp) {
        this.name = name;
        this.hp = hp;
    }
    
    public void attackBack(Ultraman u) {
        u.hp -= 10;
        System.out.println(this.getName() + "反击了" + u.getName());
    }
    
    public String getName() {
        return this.name;
    }
    
    public void status() {
        System.out.printf(this.getName() + "小怪兽 hp:%d\n", hp);
    }
}

主函数:

        Ultraman ultraman = new Ultraman("迪迦奥特曼", 500, 200);
        Monster[] monsters = new Monster[3];
        for (int i = 0; i < monsters.length; i++) {
            monsters[i] = new Monster("小怪兽" + (i + 1) + "号", 100);
        }
        Scanner input = new Scanner(System.in);
        while (ultraman.hp > 0) {
            System.out.printf(ultraman.getName() + "，请选择攻击方式: \n" + "1.普通攻击  2.发动暴击 3.魔法攻击\n");
            int attackModel = input.nextInt();
            System.out.print(ultraman.getName() + "，请选择攻击哪个小怪兽: ");
            int monsterNum = input.nextInt();
            if (monsters[monsterNum - 1].hp > 0) {
                switch (attackModel) {
                case 1:
                    ultraman.attack(monsters[monsterNum - 1]);
                    monsters[monsterNum - 1].attackBack(ultraman);
                    ultraman.status();
                    monsters[monsterNum - 1].status();
                    break;
                case 2:
                    ultraman.hugeAttack(monsters[monsterNum - 1]);
                    monsters[monsterNum - 1].attackBack(ultraman);
                    ultraman.status();
                    monsters[monsterNum - 1].status();
                    break;
                case 3:
                    ultraman.magicalAttack(monsters);
                    for (int i = 0; i < monsters.length; i++) {
                        monsters[i].attackBack(ultraman);
                    }
                    ultraman.status();
                    for (int i = 0; i < monsters.length; i++) {
                        monsters[i].status();
                    }
                    break;
                }
            }
            else {
                System.out.println(monsters[monsterNum - 1].getName() + "没有hp了，已经死亡");
            }
        }
        input.close();

• 3.改造成面向对象 围墙 过道 fencePrice aislePrice
  过道类:

public class Aisle {
    private static final double AISLE_UNIT_PRICE = 38.5;
    private double radius;
        
    public Aisle(double radius) {
        this.radius = radius;
    }

    public double area() {
        return Math.PI * this.radius * this.radius;
    }
    
    public double area(double radius) {
        return Math.PI * radius * radius;
    }
    
    public double aislePrice(double r) {
        return (this.area() - area(r))* AISLE_UNIT_PRICE;
    }
}

围墙类:

public class Fence {
    private static final double FENCE_UNIT_PRICE = 15.5;
    private double radius;
    
    public Fence(double radius) {
        this.radius = radius;
    }

    public double perimeter() {
        return 2 * Math.PI * this.radius; 
    }
    
    public double fencePrice() {
        return this.perimeter() * FENCE_UNIT_PRICE;
    }
}

主函数:

        Scanner input = new Scanner(System.in);
        System.out.print("请输入游泳池的半径: ");
        double r = input.nextDouble();
        if (r > 0) {
            Fence fence = new Fence(r + 3);
            System.out.printf("围墙的造价为: %.2f元\n", fence.fencePrice());
            Aisle aisle = new Aisle(r + 3);
            System.out.printf("过道的造价: %.2f元", aisle.aislePrice(r));
        }
        else {
            System.out.println("游泳池的半径应该是一个正数.");
        }
        input.close();